1. Field of the Invention
The present invention relates to ophthalmic photography apparatuses and ophthalmic photography methods for photographing eyes for examination.
2. Description of the Related Art
Ophthalmic photography apparatuses for acquiring an image of an eye to be examined through the use of an imaging device, such as a charge-coupled device (CCD), and then converting the acquired image into a video signal for the purpose of aligning, observing, and photographing the eye are described in, for example, Japanese Patent Laid-Open Nos. 9-262211 (corresponding to U.S. Pat. No. 6,158,864) and 10-234671.
These apparatuses are controlled so as to produce an optimal video signal from the image of the eye to be examined by electrically amplifying the signal output from the CCD.
Typically, these apparatuses have fixed control ranges of the parameters: light intensity of an illumination light source and the amplification factor of the image signal from the imaging device, where these parameters can be set to their respective maximum values.
Furthermore, ophthalmic photography apparatuses including a plurality of image-recording units and a limiting unit for limiting the upper-limit intensity of illumination light for each of the image-recording units are described in, for example, Japanese Patent Laid-Open No. 4-352934.
For fluorescein fundus angiography (or indocyanine green fundus angiography), it is difficult to determine the intensity of photographing light when attempting to record a fundus image through the use of a photography light source in the first-half stage of fluorescein fundus angiography (or indocyanine green fundus angiography) processing, particularly until an indocyanine green (or fluorescein sodium) fully circulates through the fundus blood vessels, due to a great change in the brightness of the fundus. To circumvent this drawback, a method for recording a fundus image by the use of only observation illumination light is desirable. With this method, however, the intensity of the observation light needs to be increased and the amplification factor of the video signal from the imaging device needs to be minimized in order to obtain a fundus image with a S/N ratio sufficiently high for diagnosis.
On the other hand, in the second-half stage of fluorescein fundus angiography (or indocyanine green fundus angiography) processing in which the indocyanine green (or fluorescein sodium) has fully circulated though the fundus blood vessels and fluorescence starts to disappear from the fundus blood vessels, it is relatively easy to determine the intensity of photographing light when attempting to record a fundus image through the use of the photography light source since the fundus does not exhibit a significant change in brightness. For this reason, in the second-half stage of fluorescein fundus angiography (or indocyanine green fundus angiography) processing in which fluorescence disappears from the fundus blood vessels and accordingly the fundus becomes dark, the use of photographing light, in addition to observation light, allows a fundus image with a high S/N ratio to be produced without having to set a very high amplification factor of the video signal from the imaging device. On the other hand, for the purpose of aligning the fundus, it is necessary to increase the intensity of observation light and to maximize the amplification factor of the video signal from the imaging device.
Thus, with the above-described known photography method, the observation illumination light needs to maintain the maximum light intensity allowed in the apparatus throughout the first-half and second-half stages of the fluorescein fundus angiography (or indocyanine green fundus angiography) processing. In other words, none of the above-described known ophthalmic photography apparatuses discloses the idea of changing the photography conditions, such as the light intensity of observation illumination light, depending on the status of the eye to be examined, such as whether the eye is in the first-half stage or second-half stage of fluorescein fundus angiography (or indocyanine green fundus angiography) processing, when the eye is to be photographed using a single image-recording unit.
Furthermore, a long-term examination with the maximum intensity of observation light causes the examined eye to receive high intensity observation light. This bothers the subject.